1. Field of the Invention
The present invention concerns an abrasive cleaning apparatus by a blasting process, and, more particularly, a apparatus suitable for the abrasive cleaning of small and medium size object.
2. Description of Related Art
In the prior art, the cleaning of metal and non-metal objects, especially objects with rigid surfaces on which deposits such as grease, oil and paint are deposited, is performed by means of sandblasting, which consists of projecting towards the objects, by means of pressurized air, granules of sand or of other solid material, in order to remove by abrasion all the substances that have adhered to the object to be cleaned.
Basically, a flow of pressurized air, conveyed in a Venturi tube, sucks the sand or, in general, the granular abrasive material from a tank and conveys it to a delivery nozzle from which it is discharged at high speed.
Alternatively, a pressure tank may be adopted containing the abrasive material which is then sucked from the tank and projected onto the object to be cleaned.
Some sandblasting procedures include the use of water in addition to air and the granular abrasive material, for a more efficient elimination of the particles to be removed. The operator directs the nozzle towards the object to be cleaned, thus projecting the granular abrasive material onto the surfaces of the object to be cleaned.
The sandblasters in the prior art also comprise a sandblasting booth, a vacuum suction system for the granular abrasive material, and a filtering system for the air leaving the booth.
The booth consists basically of a hollow structure provided with an access door, a glass inspection window, two holes with long-sleeved gloves, and an outlet at the bottom. The sandblasting booth is designed to accommodate the object to be cleaned and is provided with a hopper base for the outflow of the air and solid parts (particles removed and sand or granular abrasive material).
The inner portion of the booth contains the nozzle for the emission of the air and the sand or granular abrasive material.
The front wall of the sandblasting booth is provided with a glass window for checking the sandblasting process and with two gloves with sleeves, extending inside the sandblasting booth and accessible from the outside, to allow the operator to handle the sandblasting nozzle and rotate the object to be cleaned.
The feed system for the granular abrasive material is installed separately from the sandblasting booth and comprises upstream a pressurized air source and downstream at least one sandblasting nozzle housed in the sandblasting booth.
The sandblasting booth discharge hopper is connected to the suction and separation system for the fumes leaving the booth, said system being designed in such a way as to separate the solid parts (particles removed and abrasive material) from the air.
The sandblasters in the prior art have a number of disadvantages.
First, the sandblasting booths of the sandblasters in the prior art are made of bent and welded sheet metal or fiberglass.
The closed booths made of sheet metal are very noisy, as the air emitted under pressure from the sandblasting nozzle generates sound waves which are amplified by the metal walls of the sandblasting booth. Further, the sand or granular abrasive material projected onto the object to be cleaned and the metal walls of the sandblasting booth generate noise, causing the vibration of the metal walls of the sandblasting booth.
The various walls and metal and sheet metal parts are joined by welding, and the welding spots, which generally correspond to the bending corners, can be naturally porous due to the addition of filler metal during the welding process. This problem is amplified by the fact that in sheet metal welding it is not possible to add significant quantities of filler metal.
Furthermore, the gaskets employed in the prior art are subject to involuntary treatment with the abrasive jet, with a consequent rapid deterioration. After a short time the booth is no longer sealed, with consequent loss of abrasive material, which is harmful for the users. This porosity or microporosity causes also a loss of material, or water in the versions with water, which can occur even after a relatively short time of use. If the construction material employed is not stainless steel, the problem could be further accelerated due to the corrosion that occurs as a result of oxidation of the above porosity points.
If aggressive chemical agents are used in the sandblasting process, for example degreasers or solvents, the metal walls and the welding lines are affected by the action of said chemical agents, which can trigger metal corrosion or oxidation.
Closed metal booths also require skilled labor for the welding of the various internal and external supports for connecting the various parts to the structure, such as the hinges for the loading door, the brackets for the door locks, the supports for the delivery means, etc.
The objects placed inside the closed booths and turned on their various sides for cleaning may also be inadvertently pushed against the metal walls, which can be surface damaged, deformed or seriously damaged.
Further, closed booths made of metal are very heavy due to the construction material used, with consequent problems of transportation, installation and subsequent handling.
Closed booths made of fiberglass partly dampen the noise and can absorb occasional shocks, but are also affected by the abrasive action of the sand or abrasive material in granules, consequently wearing out and producing and accumulating glass dust in the hopper, in the outlet and in the filtering system.
In addition to the above problems strictly relating to closed booths, there are other disadvantages concerning the entire sandblasting system.
The various parts of the current sandblasters (sandblasting booth, suction system for sand or granular abrasive material and filtering system) constitute independent elements interconnected by ducts, pipes and cables. All these separate parts require space for installation and maintenance; furthermore the various pipes, ducts and cables hinder the transit and work of the operator.
If the operator is required to modify the sandblaster operating parameters, for example, pressure, quantity of sand or granular abrasive material, or amount of water or other liquids, he must interrupt the sandblasting operation, in order to access the suction system and make the necessary modifications.